This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-309337 filed on Oct. 5, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a starter for cranking an internal combustion engine, in which a pinion is engaged with a ring gear of the engine by pushing forward the pinion by a helical spline while restricting rotation of the pinion.
2. Description of Related Art
An example of the starter of this type is disclosed in JP-A-9-49476. This starter includes a pinion coupled with an output shaft via a helical spline formed on the output shaft and a member for restricting rotation of the pinion to push forward the pinion by the helical spline. The pinion, rotation of which is restricted by the restricting member, is released after its engagement with ring gear is established, thereby to transmit a rotational torque of an electric motor to a ring gear of the engine.
In a process of cranking up an engine, there is a possibility that a driver inadvertently restarts the starter after the engine is already started. In this case, the pinion cannot engage with the ring gear because the ring gear is rotating at a high speed. Accordingly, the pinion is forcibly rotated while its rotation is restricted by the restricting member. For allowing the pinion rotation, in the conventional starter described in the above publication, the restricting member coupling with one of plural depressions formed on an outer periphery of an annular member is forcibly and repeatedly moved from one depression to other depressions. In this movement of the restricting member, a high abrasive force is generated between the restricting member and projections formed between the depressions. Therefore, abrasion wear occurs on both of the restricting member and the projections. As the abrasion wear proceeds, the restricting member becomes unable to perform its function for restricting the pinion rotation, and thereby an operating life of the starter is shortened.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved starter having a long operating life by reducing the abrasive force imposed on the member for restricting rotation of the pinion.
The starter for cranking an internal combustion engine includes an electric motor, an output shaft driven by the electric motor and a pinion coupled to the output shaft via a helical spline. The pinion is composed of a pinion gear that engages with a ring gear of the engine to crank up the engine and an annular member integrally formed with the pinion gear. The annular member has an outer periphery, a diameter of which is larger than that of the pinion gear. Plural depressions are formed on the outer periphery of the annular member, and a rod member is engaged with one of the depressions to restrict rotation of the pinion.
The pinion coupled to the output shaft via the helical spline formed on the output shaft is pushed forward to a position engaging with the ring gear according to rotation of the output shaft. Rotation of the pinion is restricted to obtain a thrust force to push forward the pinion. After the pinion engagement with the ring gear is established, the restriction of pinion rotation is removed by separating the rod member from the depression of the annular member. Then, the engine is cranked up by a rotational torque of the pinion gear driven by the electric motor. After the engine is cranked up, the pinion is returned to its original position by a biasing force of a return spring.
Under certain situations, e.g., when the starter motor is inadvertently restarted after the engine has been cranked up, the pinion is forcibly rotated by the electric motor while its rotation is restricted. In such a case, the rod member engaging with one of the depressions has to move to other depressions overriding a projected portion between neighboring two depressions to allow the pinion to rotate. In this case, a high abrasive force is generated between the rod member and the outer periphery of the annular member, causing abrasion wear of both members.
To reduce such abrasive force, rollers are disposed between neighboring two depressions. The rod member rolls over the rollers when the restricted pinion is forcibly rotated, thereby reducing the abrasion wear of both the rod member and the annular member. An operating life of the starter is prolonged by reducing the abrasion wear.
Alternatively, instead of disposing the rollers between the depressions, the rod member may be covered with a rolling sleeve which similarly reduces the abrasive force between the rod member and the annular member. Both of the rollers and the rolling sleeve may be used to further reduce the abrasive force.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.